1. Field of the Invention.
This invention relates to organic peroxides, such as dicumyl peroxide. More particularly, the invention relates to the preparation of such organic peroxides and also to the purification thereof.
2. Description of the Prior Art.
Extensive prior art exists on the preparation of aralkyl and alkyl peroxides. The prior art can best be summarized under three major methods of preparation.
1. The acid-catalyzed condensation of a hydroperoxide with an alcohol [Milas and Harrris, JACS, 60, 2434 (1938); Milas and Surgenor, JACS, 68, 205 (1946); Milas and Perry, JACS, 68, 1938 (1946); U.S. Pat. Nos. 2,668,180 (1954), 3,254,130 (1966), 3,310,588 (1967); and 3,337,639 (1967).] This is probably the most widely known and widely used method for the preparation of alkyl peroxides. This method is best used where the product peroxide is not acid-sensitive, where the hydroperoxide is relatively stable to acid, and where the alcohol is tertiary and readily forms a carbonium ion. This method is less satisfactory when one or more of the above conditions are not met. For example, the acid-sensitivity of cumene hydroperoxide is widely known. Cumyl t-butyl peroxide can be prepared in good yield by the sulfuric acid catalyzed condensation of cumyl alcohol and t-butyl hydroperoxide but can not be prepared by the sulfuric acid catalyzed condensation of cumene hydroperoxide and t-butyl alcohol. Peroxides containing an aralkyl group are also somewhat acid-sensitive although to a much less degree than cumene hydroperoxide. Thus, dicumyl peroxide and cumyl t-butyl peroxide will decompose in the presence of mineral acids even at room temperature giving among other things phenol and acetone. Several patents (see list above) teach the preparation of dicumyl peroxide by the acid-catalyzed condensation of cumene hydroperoxide and cumyl alcohol; we have found such processes to be unsatisfactory and very hazardous.
2. The acid-catalyzed addition of a hydroperoxide to an olefin [Milas and Harris; Milas and Surgenor; Davies et al., J. Chem. Soc., 2200 (1954) and U.S. Pat. No. 3,267,066 (1967)].
This process has the same advantages and disadvantages of (1) above. It is generally used with olefins which readily form tertiary carbonium ions such as the acid-catalyzed addition of t-butyl hydroperoxide to isobutylene or diisobutylene. It is less satisfactory for olefins like .alpha.-methylstyrene which readily undergo acid-catalyzed telomerization. U.S. Pat. No. 3,267,066 shows the preparation of dicumyl peroxide from .alpha.-methylstyrene, cumene hydroperoxide and hydrogen chloride.
3. The displacement reaction between an alkali metal salt of a hydroperoxide and an alkyl halide [U.S. Pat. No. 2,403,709 (1946), T. W. Campbell and G. M. Coppinger, J. Am. Chem. Soc., 73 1789 (1951), and U.S. Pat. No. 3,247,259 (1966).] This is an especially good method for the preparation of peroxides from primary or secondary halides or sulfates but is of dubious value for tertiary halides since dehydrohalogenation is far more rapid than the displacement reaction.
4. There are several processes for the preparation of specific peroxides. Dicumyl peroxide is formed as a minor byproduct of the autoxidation of cumene to cumene hydroperoxide. It is not a practical process for the preparation of dicumyl peroxide but represents a by-product of large scale producers of phenol from cumene.
Another method of preparation of aralkyl peroxides is the copper ion-catalyzed decomposition of hydroperoxides in the presence of substrates. Thus cumyl t-butyl peroxide (60% yield) can be prepared by heating at 67.degree. for 18 hours a mixture of cumene, t-butyl hydroperoxide and cuprous chloride. However, the stoichiometry requires the consumption of two moles of hydroperoxide for each mole of peroxide produced. Thus only 30% of the hydroperoxide is converted to peroxide in this reaction.